A primary purpose of this work is to investigate the relationship between age and concentrative ability. Using laboratory studies of task-unrelated imagery and thought (TUIT) it was determined that old adults had fewer TUITs than young and middle-aged adults. One possible explanation for this result is that age and concentrative ability are directly related. Laboratory investigations are needed to confirm this apparent increased concentrative ability in the older population. An experimental procedure was developed where subjects are asked to repeat messages presented to one ear (shadowing) while ignoring simultaneous messages in the other ear. High concentrative ability is demonstrated by equivalent shadowing performance with and without simultaneous (and different) messages in the other ear. An experimental study using young (18-29 yrs), middle-aged (40-55 yrs) and old (65-85 yrs) subjects was completed. After controlling for differences in intelligence, hearing loss, and monaural shadowing performance it was determined that age and concentrative ability are inversely related. With increased age there was an increase in dichotic shadowing errors. The decrease in concentrative ability with increased age was also evident when the sample was restricted to those who did not take prescription medication and were not hospitalized within the prior two years and when the sample was restricted to those who made no monaural shadowing errors.